During surgery it is preferred that the muscles of the patient be as relaxed as possible. Although general anesthesia renders the patient unconscious, it only rarely provides sufficient skeletal muscle relaxation. A variety of muscle relaxant agents, also known as neuromuscular blocking agents, are used for muscle relaxation during surgery. One muscle relaxant used frequently in the past is succinylcholine, which has a very rapid onset and short duration of clinical action. However, succinylcholine elicits muscle membrane "depolarization" which makes this compound less desirable. Furthermore, it may produce serious side effects.
Several other so called "non-depolarizing" muscle relaxants are known and used in anesthesia and surgery. These chemically diverse non-depolarizing muscle relaxants include, among others: tubocurarine, pancuronium, atacurium, cisatacurium, vecuronium, mivacurium and rocuronium. The common structural feature of these compounds is one or usually two quaternary nitrogen atoms. They are all clinically acceptable because they produce only milk or no side effects. However, their onset of action is too slow and their duration of action is too long. Thus, these agents, without exception, fall short of the requirements of an "ideal" surgical muscle relaxant.
Hungarian Patent No. 142,597 issued on Sep. 15, 1955, discloses a series of compounds having a pair of tropine moieties bound by an ester linkage to an aliphatic or aromatic diacid. The nitrogens on both tropines are quaternized with alkyl or unsubstituted or monosubstituted benzyl groups.
Certain naturally occurring alkaloids consist of dicarboxylic acid esters of azabicyclo alkanols, such as belladonnine, which is a bis tropinester, and thesine, which is a bis oxymethyl pyrrolizidine ester. Only the ethyl quaternary derivative of belladonnine and the methyl quaternary derivative of thesine have been reported as muscle relaxants.
Some other neuromuscular blocking agents that include pairs of quaternary nitrogens as part of a tropane ring system have been reported in the literature. In these compounds tropinyl moieties are joined by bridging the two quaternary nitrogens. U.S. Pat. No. 2,746,964 (1953) discloses dicarboxylic acid esters of 3-piperidinol and their alkyl quaternary derivatives.
It is an object of the present invention to provide new and improved muscle relaxants which are characterized by very rapid onset and short duration of neuromuscular blocking action.